This research will investigate brain electrical potentials or averaged auditory cortical evoked responses (ERs) in eighty healthy middle aged and elderly men and women and twenty senile dementia patients. In healthy volunteers brainstem evoked responses (farfield acoustic responses), auditory evoked responses elicited in sensory set and later components of ERs (e.g., the late positive component or P3 wave and the contingent nagative variation) in a response set will be studied within subjects in relation to age and ability to pay attention as indexed by reaction time. In senile dementia patients brainstem evoked responses and auditory evoked responses will be evaluated in relation to degree of impairment of cognitive function. Cognitive function will be defined by psychiatric and psychological evaluation or orientation, memory, and intellectual intactness. A multivariate approach will be taken to assess the relationships of brain electrical potentials to age, sex, and attentional deficit and presence of dementia.